1. Field of the Invention
The present invention relates in general to the field of electronics, and more specifically to power conversion with controlled capacitance charging that includes a dimmer attach state control.
2. Description of the Related Art
Many electronic systems utilize switching power converters to convert power from one source into power useable by a load. Additionally, many electronic systems also utilize dimmers that cause a controller of the switching power converter to modify output power delivered to the load depending on a dimming level. For example, in a lighting system, dimmers provide an input signal to a lighting system, and the load includes one or more light sources such as one or more light emitting diodes (LEDs) or one or more fluorescent light sources. The dimming level from the dimmer causes the lighting system to adjust power delivered to a lamp, and, thus, depending on the dimming level, increase or decrease the brightness of the lamp. Many different types of dimmers exist. Many common analog based dimmers utilize a triode for alternating current (“triac”) device to modulate a phase angle of each cycle of an alternating current (“AC”) supply voltage. “Modulating the phase angle” of the supply voltage is also commonly referred to as “chopping” or “phase cutting” the supply voltage. Phase cutting the supply voltage causes the voltage supplied to a lighting system to rapidly turn “ON” and “OFF” thereby controlling the average power delivered to the lighting system.
FIG. 1 depicts a lighting system 100 that includes a phase cut dimmer 102. The phase-cut dimmer 102 can be any type of dimmer, such as a leading edge, trailing edge, or center-cut dimmer A triac-based leading edge dimmer is described in the Background section of U.S. patent application Ser. No. 12/858,164, entitled Dimmer Output Emulation, filed on Aug. 17, 2010, and inventor John L. Melanson. The lighting system 100 receives an AC supply voltage VSUPPLY from voltage supply 104. The supply voltage VSUPPLY, indicated by voltage waveform 202, is, for example, a nominally 60 Hz/120 V line voltage in the United States of America or a nominally 50 Hz/230 V line voltage in Europe. The phase-cut dimmer 102 phase cuts the input voltage VIN to generate the phase-cut input voltage VΦ—IN, and a full-bridge diode rectifier 106 rectifies the phase-cut input voltage VΦ—IN to generate the phase-cut, rectified, line input voltage VΦ—DIM.
The lighting system 100 also includes a controller 112 that generates a control signal CS0 to control the voltage VΦ—DIM into an output voltage VLED by a switching power converter 108. The switching power converter 108 can be any type of switching power converter. Many types of switching power converters exist. In general, switching power converters include a capacitor 114 or multiple additional capacitors (not shown) at the input of the switching power converter, a capacitor 116 within the switching power converter, and/or a capacitor 118 at the output of the switching power converter. For example, a first stage of a two stage switching power converter is typically a boost switching power converter but can also be a buck or transformer coupled stage. The second stage is, for example, a flyback, buck, or other topology, such as a resonant topology. Two stage switching power converters generally include a high frequency, electromagnetic interference capacitor at an input of the switching power converter and a link capacitor after the first stage. The capacitors store energy to smooth out the transfer of power to the load 110, and the amount of smoothing generally depends upon the capacitor size and switching power converter topology. Two stage switching power converters are flexible but generally include more components than single stage switching power converters. Thus, two stage switching power converters are generally more expensive.
A single stage switching power converter converts power directly from the phase-cut, rectified voltage VΦ—DIM into a direct current (DC) voltage for the LED(s) 110. Single stage switching power converters are, for example, flyback, buck, or boost-buck type switching power converters. The single stage switching power converters generally include one large, energy storage capacitor at location 118, and the size of the capacitor generally increases as efficiency of the LED(s) 110 increases due to the dynamic impedance of a high efficiency LED(s) 110. Peak-rectified type switching power converters include a large capacitor at the input of the switching power converter that stores energy for each cycle of the rectified voltage VΦ—DIM. Peak rectified switching power converters are generally relatively inexpensive. However, the power factor of a peak-rectified switching power converter is generally worse than other single stage and two stage switching power converters, and ripple stress on the energy storage capacitor tends to be relatively high. Additionally, compatibility between the switching power converter 108 and/or efficiency is also compromised when using conventional peak-rectified switching power converters.